Computers are ubiquitous in today's society. Computers of all types are used to perform a variety of tasks. Computers accomplish tasks by processing software applications. Software applications are programs that allow a user to interface with and perform one or more tasks on a computer system. In order to function efficiently, software applications are generally installed in the computer's operating system. An application can be installed either machine-wide, in which case it is available to all users of a particular computer, or per-user, in which case it is available only to a single user (typically the user who installed the application). Typically, in an effort to keep the operating system secure, the operating system limits the type of computer users that are allowed to install applications machine-wide. Users that are allowed to install applications machine-wide (i.e., that have sufficient privileges) are often referred to as administrators, or in some cases, power users.
Allowing all users to install applications machine-wide is typically not desirable since untrained and/or malicious users could install applications that detrimentally affect the operating system, the computer system, and/or the data belonging to any user who runs the application. For example, unwanted applications, such as viruses or spyware, can cause damage to the operating system, the computer system, and/or the data belonging to any user who accidentally runs them. Thus, limiting the type of users that have sufficient privileges to install applications machine-wide can limit the risk of malicious applications being able to affect all users of a computer.
Unprivileged users therefore typically will install applications in a per-user fashion, such that the applications are available only to the user who installed them. This leads to several issues.
For example, consider the case where multiple unprivileged users each install Application Z. The computer will have multiple versions of Application Z installed—one version for every user that installed Application Z. This places a heavy burden on computer resources such as hard disk space. Furthermore, if an issue is discovered with Application Z that requires an update, each user's copy of Application Z must be updated, either by the users themselves or by an administrator.
Furthermore, in cases where multiple unprivileged users are simultaneously using an application that was separately installed by each unprivileged user, the computer allocates a portion of random access memory (RAM) for each user. Such allocations of RAM can severely affect the computer's ability to efficiently process the application for each user.